DVD +-RW DL Drive will NOT burn RW Discs - **Bizzare**

So I was sitting in the workshop yesterday and a customer came in with a problem...
He could not burn RW disc's, Cd or DVD, But could burn other disc's fine...

SPECS

Asus P5b MainBoard
512 Dual-channel DDR2 667
Core 2 Duo
LG DVD +-RW DL Multi Drive
SATA Western Digital 120GB

XP Home
Only Loaded drivers and AVG



So..

I changed the cables... No change
Changed the drive... No change
Updated FIRMWARE For BIOS and Drive... No Change
Changed IDE Channels... No change...
Changed the RAID IDE settings in every possible way... No change
Removed the drive and tried it in another computer... VOILA... Works

So Its not the drive... Nor the BIOS as both mainboards are the same and running same FIRMWARE plus same version... Plus have EXACTLY THE SAME HARDWARE!!!...

So I thought I had it figured...

I changed the mainboard and... No Change...
I Removed the Hard-Disk, Installed a fresh partition and OS... No change
Removed all un-needed hardware... No change...
Disabled on-board sound, usb, SATA(Connection at the Back Plate) and LAN... No change
Tried another 5 Drives, all different brands and still... NO CHANGE!!!
Replaced the Power Supply... No change...
Replaced the Processor... No change...
Flashed the BIOS... No change
Reloaded FIRMWARE... No change...
Replaced the Hard Disk... No change...





I have replaced every part in this PC and it still wont burn to RW... Software is fully compatible and the same hardware, used in anyother CASE will work...

IS THE CASE THE PROBLEM?? Because nothing is wrong with anything else...

Help.... Please...